This invention relates to a method of segmenting an electrical signal derived from an acoustic signal in which, consecutively,
a number of parameters is derived from the electric signal as a function of time, PA1 the signal, of the parameters located within a time interval around each instant are taken up for consecutive instants, PA1 a transition function .0. is determined for each instant from the signals of the parameters located within the associated time interval, and PA1 information relating to the segments from which the acoustic signal is built up is derived from the transition functions associated with the instants. PA1 first means for deriving a number of parameters from the electric signal as a function of time, and PA1 second means for deriving a transition function for each instant from the signals of the parameters located within the associated time interval, is characterized in that the device also comprises PA1 a first memory for storing the transition functions, PA1 third means for calculating a similarity factor between two transition functions associated with respective proximate instants i and j, PA1 a second memory for storing the similarity factors, and PA1 fourth means for deriving the replacing or combined transition function from the transition functions of at least one group of transition functions for which the associated similarity factor is larger than a reference value.
The invention also relates to a device for performing the method,. A method of the type defined in the opening paragraph is disclosed in PTC Application No. WO 84/04194.
The Application describes a temporal decomposition method by B. S. Atal for economically coding and subsequently transmitting speech, which method determines the acoustic vectors and their associated transition functions for an utterance. Atal describes a procedure for determining a transition function which is most centrally located in a certain time interval. Consecutive transition functions can be determined by shifting the time interval over small time steps. For a detailed description of the method reference is made to the publication "Efficient coding of LPC parameters by temporal decomposition" by B. S. Atal in ICASSP 83, the proceedings pp. 81-84 and to the publication "Temporal decomposition of speech" by S. M. Marcus et al, 1984 IPO annual progress report no. 19, page 25 etc.
Atal's method uses a mathematical procedure yielding transition functions (and associated acoustic vectors) which in practice show little resemblance to phonetically relevant events in the speech signal.
E. A. Zuk has found that the known method has a considerable drawback which becomes particularly manifest if phonetically relevant events in the speech signal were to be fixed by means of the known method, see E. A. Zuk "An investigation of temporal decomposition of speech parameters for automatic segmentation of Speech", IPO report No. 459. Zuk found that small variations in, for example, the length of the time interval had a great influence on the transition functions obtained by means of the known method. Particularly if a physical relationship is desired between acoustic vectors from which the speech signal is built up and phonetically relevant events in the speech signal, this great influence is very undesirable. In fact, it would mean that a different choice of the length of the time window at a given instant during the speech signal would lead to a different acoustic vector in the relevant time window.